Implantable seizure warning system

ABSTRACT

Techniques for warning a patient of a possible onset of a seizure using a sensor, a signal generator and at least one implantable electrode. The electrodes are positioned to stimulate the spinal cord or under the skin. The sensor senses a parameter of the body indicative of the possible onset of a seizure. The sensor generates a sensing signal which is processed and an algorithm is utilized to determine whether the sensing signal shows a pattern indicative of a possible seizure onset. If such a pattern is recognized, the signal generator provides electrical stimulation via electrodes to generate a sensory stimulus to the body. The stimulation may provide visual, aural or touch stimulus to the patient. The patient is thereby alerted to the possibility of a seizure onset and may take appropriate action.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the treatment of seizure disorders and, andmore particularly relates to techniques for warning patients of anepileptic seizure.

2. Description of Related Art

Epilepsy is a condition characterized by recurrent seizures which arethe outward manifestation of excessive and/or hyper-synchronous abnormalelectrical activity of neurons in the cerebral cortex of the brain. Aseizure often occurs when the electrical activity of the brain becomesmore "synchronized" as would be the case when the person is in a drowsystate.

A seizure patient may suffer from any combination of different types ofseizures. Grand mal seizures are the most common form of epilepsy andare characterized by convulsions with tonic-clonic contractions of themuscles. Absence seizures (previously referred to as "petit mal") arecharacterized by a brief and sudden loss of consciousness. Thepsychomotor form of seizures is characterized by a clouding ofconsciousness for one or two minutes. A complex partial seizure ischaracterized by a complete loss of consciousness. The type of seizureexperienced is typically dependent upon the function of the portion ofthe cerebral cortex where hypersynchronous activity is occurring. Manytypes of seizures generally involve the entire brain, while certaintypes, such as partial seizures, begin in one part of the brain and mayremain local.

Regardless of the type of epilepsy, seizures significantly limit theautonomy of the patient. When hit with a seizure attack, the patienttypically loses some level of control of his/her body. In most cases,seizures occur without prior warning to the patient. As a result,epileptic seizures pose a serious safety hazard to the patient as otherssurrounding the patient. For example, a patient hit with a suddenseizure attack while he/she is driving a car may endanger his/her ownsafety as well as the safety of others. Seizure patients are alsoexposed to a risk of bodily harm when operating machinery and even indaily activities such as crossing a street or going down stairs.

Researchers have developed a number of techniques for treating seizuredisorders and its symptoms. For example, research has shown thatinhibiting (namely, reducing the excitation of neurons) the substantianigra in the brain increases the threshold for seizure occurrence.Researchers have also found that increasing the activity of neurons inthe external Globus Pallidum (GPe) increases inhibition of neurons inthe subthalamic nucleus which in turn inhibits neural activity in thesubstantia nigra. Neurosurgeons have also been able to diminish thesymptoms of many neural disorders by lesioning certain brain areas,examples being lesioning the ventral lateral portion of the internalGlobus Pallidus and the Vim Thalamus for treating movement disorders.Alternatively, it has been demonstrated that open-loop Deep BrainStimulation (DBS) at high frequencies (100 Hz or higher) of certainbrain structures can alleviate, diminish, or completely stop symptoms oftremor, rigidity, akinesia or hemiballism much like creating a lesion.Electrical stimulation of the nervous system has also been used tosuppress seizures. Finally, infusion of certain drugs into a region ofthe brain can affect the excitability of the neurons at the site ofinfusion as disclosed in U.S. Pat. No. 5,713,923 (Rise et al.) assignedto Medtronic, Inc.

Others have studied the effects of electrically stimulating the vagusnerve as a means of "desynchronizing" the electrical activity of thebrain. It has been observed that stimulation of the vagus nerve withcertain parameters caused de-synchronization of the brain's electricalactivity in animal models. These concepts were disclosed by Zabara inU.S. Pat. Nos. 4,867,164 and 5,025,807. De-synchronization can bethought of as "alerting" phenomena since it reflects active mentalactivity.

Under another approach, researchers have devised algorithms to detectthe onset of a seizure. Qu and Gotman reported a system that recognizespatterns of electrical activity similar to a template developed fromrecording an actual seizure. See H. Qu and J. Gotman, "A Seizure WarningSystem for Long-term Epilepsy Monitoring", Neurology, 1995;45:2250-2254.Similarly, Osario et. al. have reported an algorithm applied to signalsrecorded from intracranial electrodes capable of 100% seizure detectionrate with 0% false negatives and minimal false positives. See I. Osario,M. Frei, D. Lerner, S. Wilkinson, "A Method for Accurate AutomatedReal-time Seizure Detection", Epilepsia, Vol. 36, Suppl. 4, 1995. Ineach of these techniques for recognizing the onset of a seizure, thedevelopers employ two processes. The first process is to extract certainfeatures from the signals representing the electrical activity of thebrain. Examples of the signal features include the signal power or thefrequency spectrum of the signals. The second process is to recognize apattern or set of values for those features which characterize a brainstate that will reliably lead to a seizure.

Using these pattern recognition techniques, researchers have developedwarning systems to alert the seizure patient of a possible seizureonset. For example, U.S. Pat. Nos. 3,863,625 and 4,566,464 discloseepileptic seizure warning systems producing audio and visual warningsignals to the patient prior to the possible onset of a seizure. Thewarning devices are external devices which can be worn in a shirt pocketof a seizure patient. Such an approach is generally simpler in designthan the above-described techniques for treatment of seizures andprovides the patient prior warning of a possible seizure onset.Advantageously over the above-mentioned methods, these device allows thepatient to take appropriate action to minimize physical injury to thepatient and others. This approach, however, requires the patient toconstantly carry around the monitoring device causing inconvenience tothe patient especially if the monitoring device is misplaced. The use ofaudio and visual signals as the warning mechanism may also not be aseffective if the device is buried underneath a heavy coat or is outsideof the hearing range of the patient. In addition, this device isineffective for seizure patients who have impaired vision or hearing.

The present invention is directed to overcoming the disadvantages of theforegoing systems.

SUMMARY OF THE INVENTION

As explained in more detail below, the present invention overcomes theabove-noted and other shortcomings of prior techniques for warning ofepileptic seizures.

A preferred form of the invention consists of a sensing portion capableof detecting the onset of a seizure, a signal processing portion, and atherapy delivery portion. The sensing portion may be an electricalsensor, chemical sensor, and/or a sensor for sensing physiologicalchanges. The particular structure and parameter to measure may beselected from any known techniques which provide indication of thepossible onset of a seizure. The signal processing portion processes andanalyzes the sensed signal using an algorithm for recognizing a patternscheme indicative of the onset of a seizure. If a pattern indicative ofthe onset of a seizure is recognized, the therapy delivery portion istriggered. The therapy delivery portion is preferably a stimulationelectrode which delivers sensory stimulation to the patient therebyalerting the patient of the onset of a seizure.

Sensory stimulation may encompass any combination of touch, sight orsound stimuli. The patient may then take appropriate action to avoidphysical injury. For example, if the patient is driving a car whenhe/she is given a warning signal under the present invention, thepatient may immediately stop the car. Further, research has found thatthe human body is capable of aborting seizures through sensory selfstimulation. For example, some patients who have a sensory experienceassociated with a partial seizure, called an aura, will slap themselvesto prevent the generalized seizure that normally follows. Accordingly,under the present invention, if a patient is provided sensorystimulation warning the patient of the possibility of a seizure onset,the patient may take similar action to prevent the seizure. In fact, ifthe sensory stimulation is sufficiently intense, it may obviate the needfor the patient to do anything since the sensory stimulation isequivalent to slapping themselves. Moreover, the cognitive recognitionof the possibility of a seizure may in itself serve to abort theoccurrence of the seizure. For example, the patient may engage in amental activity such as performing mathematical computations to"de-synchronize" the neurons, thereby reducing the hypersynchronous ofthe neurons.

Under another embodiment, the invention includes a sensing portion, asignal generating portion and a therapy delivery portion. Under thisembodiment, the sensing portion monitors electrical, chemical and/orphysiological activity of the patient. The signal generating portiontransduces the sensed activity of the patient to a correspondingelectrical signal. The therapy delivery portion provides sensorystimulation to the patient based on the electrical signal provided bythe signal generating portion. Sensory stimulation may be provided bystimulation of the dorsal column of the spinal cord. Alternatively itmay be provided by stimulation of a region of the thalamus or cortexrepresenting a sensory function such as skin sensation or sound, visualor olfactory perception. The patient is thereby provided continuoussensory stimulus relating to electrical, chemical and/or physiologicalactivity of the patient sensed by the sensing portion. Before thepatient experiences a seizure, the patient will have sensed a certainpattern of sensory stimulus. After one or more of such seizure episodes,the patient may thereby learn to recognize patterns which are indicativeof a seizure onset. By recognizing these patterns, the patient maythereby take appropriate action as discussed herein.

By using the foregoing techniques, seizure disorders, includingepilepsy, can be treated and seizures can be alleviated or preventedusing sensory stimulation to consciously alert the patient of the onsetof a seizure. By alerting the patient of a possible seizure onset, thepatient may take action to minimize the risk of injury result from aloss of bodily control. Moreover, mental awareness by the patient of thepossibility of a seizure in itself may thereby prevent the seizure fromoccurring.

Examples of the more important features of this invention have beenbroadly outlined above in order that the detailed description thatfollows may be better understood and so that contributions which thisinvention provides to the art may be better appreciated. There are, ofcourse, additional features of the invention which will be describedherein and which will be included within the subject matter of theclaims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages and features of the invention will becomeapparent upon reading the following detailed description and referringto the accompanying drawings in which like numbers refer to like partsthroughout and in which:

FIG. 1 is a diagrammatic illustration of a preferred embodiment of thepresent invention having a sensor implanted in a brain, a signalgenerator and stimulation electrodes;

FIG. 2 is a diagrammatic illustration of the embodiment of FIG. 1depicting the placement of the stimulation electrodes to stimulate apredetermined site of the spinal cord;

FIG. 3 is a block diagram of the signal processing portion of thepresent invention; and

FIG. 4 is a flow chart depicting the steps for alerting the patient of apossible seizure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention discloses techniques for providing sensorystimulation as a means for desynchronizing the electrical activity ofthe brain which leads to a seizure. As preferred, the invention includesgenerally a sensor portion for monitoring the onset of a seizure, asignal processing portion for processing the sensed signals to recognizea pattern indicative of a seizure onset, and a therapy delivery portionfor providing sensory stimulation to alert the patient of the possibleonset of a seizure.

Referring to FIGS. 1 and 2, a system made in accordance with thepreferred embodiment may be implanted below the skin of a patient. Thesystem includes generally a sensor 20, a signal processor/generator 30and one or more stimulation electrodes 40.

Sensor 20 serves as the sensing portion of the present invention. Sensor20 is implanted into a portion of a patient's body suitable fordetecting a condition resulting from the onset of a seizure, including aseizure itself. Sensor 20 is adapted to sense an attribute of the bodythat changes in advance of or during a seizure. Sensor 20 is operativelycoupled to provided sensed signals to the signal processor/generator 30.As shown, sensor is coupled via lead 25 to signal processor/generator30. Alternatively, telemetry may be used to couple components 20 and 30.Signals that are received by the sensor may by amplified beforetransmission to signal processor/generator 30.

Sensor 20 may take the form of a device capable of detecting nerve cellor axon activity that is related to the pathways at the cause of aseizure symptom, or that indicates sensations which are elicited by theonset of a seizure. As preferred, sensor 20 is located deep in the brainparachyma in appropriate locations as shown in FIG. 1 and consists of atube 50 implanted into brain B that carries one or more depth wireelectrodes near end 52 of tube 50. For such detecting, the electrodesmay be inserted into the thalamus, internal capsule, hippocampus, cortexor basal ganglia of brain B. Alternatively, the electrodes may beinserted into the seizure focus or part of the central nervous systemwhere seizures begin.

In other embodiments, sensor 20 may include electrical transducersincluding subcutaneous electrodes placed on the surface of the skullover appropriate brain structures, peg electrodes implanted into theskull over these brain structures, epidural electrodes, or subduralelectrodes placed on the cortical surface of appropriate brainstructures. Under these embodiments, brain EEG/ECoG recorded above thecortical surface also may be detected by such a sensor. Sensors placedabove the cortical surface may be generally located at two or morelocations identified in the International 10-20 system of standard sitesfor EEG (Spehlmann's EEG Primer, Second Edition, Bruce J. Fisch,Elsevier Sciences Publisher BV, 1991).

Alternatively, sensor 20 may be a chemical sensor implanted in the brainB or ventricular space for detecting certain chemical substances such astransmitter substances or the break down products of transmittersubstances. Under this alternative, sensor 20 may take the form of atransducer consisting of an electrode with an ion selective coatingapplied which is capable of directly transducing the amount of aparticular transmitter substance or its breakdown by-products found inthe interstitial space of a region of the brain B such as thehippocampus or thalamus. The level of the interstitial transmittersubstance is an indicator of the relative activity of the brain regionand the onset of a seizure. An example of this type of transducer isdescribed in the paper "Multichannel semiconductor-based electrodes forin vivo electrochemical and electro-physiological studies in rat CNS" byCraig G. van Horne, Spencer Bement, Barry J. Hoffer, and Greg A.Gerhardt, published in Neuroscience Letters, 120 (1990) 249-252.

As yet another alternative, sensor 20 may sense physiological changeswhich are indicative of a seizure onset. For example, sensor 20 maytransduce physiological changes in the heart rate or respiration. Underthis alternative, sensor 20 may be placed near nerve cells controllingmuscles and include a device capable of detecting nerve compound actionpotentials (e.g., either sensory afferent information from muscle orskin receptors or efferent motor potentials controlling a muscle ofinterest). Alternatively, sensor 20 may detect muscle EM& in one, two ormore muscles. Monitored muscles may include the heart, respiratorymuscles or reciprocal muscles at one joint. For such detection, sensor20 may take the form of a lead with one or more recording electrodesinserted into the muscle of interest. In yet other embodiments, sensor20 may sense heart rate or respiration rate. Sensor 20 may be physicallylocated outside of the body and communicate with the implanted portionthrough telemetry.

The output of sensor 20 is coupled by cable 25, comprising one or moreconductors, to the signal processing portion of the present invention.Alternatively, the output of an external sensor would communicate withthe implanted pulse generator through a telemetry downlink. Suchtelemetric systems may use, for example, radio frequency, ultrasound,infrared or other like communication means.

The signal processing portion of the present invention is preferablyincluded within signal processor/generator 30. Alternatively, signalprocessor/generator 30 may be separated into a signal processingcomponent and a signal generating component. The signal processingportion or component provides a means for signal processing and meansfor pattern recognition. FIG. 3 is a block diagram depicting the signalprocessing portion of the present invention. A signal received fromsensor 20 may be processed by amplifying and filtering the signal byamplifier 100 and filter 200 respectively. The signal is then convertedto a digital representation by analog to digital converter 300. Thesignal may then be further processed by a digital signal processing chip400 or may be input to a microprocessor 500. Microprocessor processesthe sensor data in different ways depending on the type of parameterthat is sensed by sensor 20. Microprocessor 500 processes the sensorsignal and determines whether there exists a threat of a seizure. Inparticular, microprocessor 500 serves as the means for featureextraction and for pattern recognition. Alternatively, digital signalprocessing chip 400 could be used to extract features prior toprocessing by the software algorithm of microprocessor 500. Featureextraction and pattern recognition involves implementing an algorithm todetect the onset of a seizure.

In a preferred embodiment, the software algorithm is performed asfollows. Sixteen channels of EEG waves are recorded. These EEG waves arethen low-pass filtered at 70 cycles/sec with a 4-pole analog filter andthen sampled at 200 samples/sec/channel. The resulting signal is thenbroken down into simple features by reducing the sinusoidal EEG signalinto a sequences of segments. A segment is a section between twoconsecutive extremes of amplitude and is characterized by duration,amplitude and direction (i.e., slope of the line). A sequence ofsegments is created to eliminate small amplitude "noise" (beta frequencyEEG, muscle artifact). This noise creates smaller intervening segmentsthat face an opposite direction to that of the neighboring largersegments. The sequence combines one or more segments which are faced inthe same direction and smaller intervening segments. A sequence endswhen a segment not belonging to that sequence is produced. A segmentdoes not belong to a sequence when its direction is opposite to theprevious segment and its length is greater than the length of theprevious segment. When a sequence is complete, the following operationstake place sequentially to determine whether a possible EEG spike orsharp wave (SSW) is detected. First, the relative amplitude of thecurrent sequence and of the preceding one is checked to determinewhether they are above a certain threshold. The relative amplitude isthe amplitude of the sequence relative to the average amplitudes of thesequences 5 seconds prior to the instant sequence. The relativeamplitude is the ratio of the amplitude of the instant sequence to theaverage amplitude of the previous sequences taken 5 seconds prior. Ifthe relative amplitude is above 4, then the sequence is marked as beingpart of a SSW. Next, the pseudo-duration of the segment is checked. Thepseudo-duration is graphically determined by extending a line from thestart of a sequence (point A) through the half-way point of the actualEEG wave and extending it so its end (point B) equals the amplitudelevel of the ending point of the sequence. The horizontal distance fromA to B is the pseudo-duration. The sequence is marked as a possible SSWif the pseudo-duration in combination with the relative amplitudereaches above a certain amount. Generally, the shorter thepseudo-duration, the lower the relative amplitude needs to be for a SSWmarking. Next, the relative amplitudes are checked in relation to therelative sharpness of the waves. The relative sharpness of the wave isthe second derivative of a wave at 15 msec before and after the apex ofa wave. The higher the relative sharpness, the lower the relativeamplitude required to mark the sequence as a possible SSW. Finally, thetotal duration of the wave is checked. If it is larger or equal to 35msec, the sequence is marked as a possible SSW.

Once a sequence or a wave is marked as a possible SSW, furtherprocessing is required to possibly reject this wave. For example, thewave is rejected if it is the result of muscle activity, eye blinks oralpha activity. Muscle activity may cause a large number of highamplitude segments in the immediate surrounding of the wave (1/3 sec).Eye blinks may cause SSW marking from an EEG in the frontal channelhaving positive polarity, has a duration larger than 150 msec, and awave of similar amplitude occurs simultaneously on the homologouscontralateral channel. Alpha activity causes a dominant frequency of8-12 cycles/sec.

Once a wave is determined to be a SSW, its relationships with otherchannels are important for localization of an epileptic focus. The aboveanalysis proceeds by discrete time units of about 1/3 sec. If severalSSWs are found in a given channel during a time unit, only the sharpestis -retained. If SSWs are found in one or more channels within the timeunit, an event is said to have occurred. The events from the 16 EEGchannels may then be tabulated. Based on the location and occurrencefrequency of these events, electrical activity indicating a seizurepattern may be determined. Such a system may be that disclosed by J.Gotman and P. Gloor in Automatic Recognition and Quanitification ofInterictal Epileptic Activity in the Human Scalp EEG,Electroencephalography and Clinical Neurophysiology, 41: 513-529, 1976.The rhythmicity of the electrical activity could also be used toindicate the occurrence of a seizure. The time interval associated withtwo successive segments is proportional to the frequency of EEGactivity. Frequency of EEG activity between 3 to 20 cycles/sec sustainedfor a sufficient duration indicated the occurrence of a seizure. Forexample, once a patient suffers a seizure attack, a template may becreated which can be used to detect future seizures exhibiting similarEEG activity. Such a template would be patient specific.

Other examples of algorithms to detect the onset of seizures have beenreported in U.S. Pat. No. 5,311,876 (issue May 17, 1994) and U.S. Pat.No. 5,349,962 (issued Sep. 27, 1994) and by Jean Gotman in EpilepsySurgery, ch. 36 (ed. Hans, Luders, Raven Press, New York 1991) and IvanOsorio & Mark Frei in Abstracts of the American Epilepsy Societymeeting, 1995. These references are incorporated herein by reference.Those skilled in the art will appreciate that any number of otheralgorithms may be used. An external electronic device may be implementedto telemeter parameter changes or newer algorithms to the implantedsignal processing device to adapt the detection algorithm to theparticular patient.

Microprocessor 500 is coupled to signal processor/generator 30 and cuesthe signal processor/generator 30 to generate a signal when a patternindicative of a seizure is identified. Signal processor/generator 30 isimplanted in a human body in a subclavicular, subcutaneous pocket.Alternatively, the signal processor/generator 30 may be implantedelsewhere, such as in the abdomen. Signal processor/generator 30 maytake the form of a modified signal generator Model 7424 manufactured byMedtronic, Inc. under the trademark Itrel II which is incorporated byreference. Signal processor/generator 30 may include a frequencygenerator, a digital to analog converter, and a pulse width controlmodule to vary the type of stimulation to provide as a warning. Thestimulus pulse frequency is controlled by programming a value to theprogrammable frequency generator (not shown). The programmable frequencygenerator provides an interrupt signal to signal processor/generator 30when each stimulus pulse is to be generated. The frequency generator maybe implemented by model CDP1878 sold by Harris Corporation.

At the time the present invention is implanted within the patient, theclinician programs certain key parameters into the memory of theimplanted device or may do so via telemetry. These parameters may beupdated subsequently as needed. Alternatively, the clinician may electto use default values. The clinician must program the range of valuesfor pulse width, amplitude and frequency which microprocessor 500 mayuse to optimize the therapy. Stimulus parameters can be adjusted (viatelemetry) by a computer algorithm within a range specified by theclinician in an attempt to optimize the seizure suppression.

FIG. 4 discloses a flow chart for providing a patient with a seizure inaccordance with the present invention. At step 405, sensor 20 senses aparameter of the body and generates a signal. At step 410, the signal isprocessed and, at 415, an algorithm determines whether the sensed signalindicates that there exists a risk of a seizure onset. This step iscontinually performed. If it is determined that a seizure onset ispossible, at step 420, electrodes 40 provide electrical stimulation toprovide some sort of sensory stimulus to alert the patient.Alternatively, the sensory stimulus may be strong enough such that it initself may abort the onset of a seizure.

Simulation electrodes 40 serve as the therapy delivery portion of thepresent invention. Each electrode 40 is individually connected to thesignal processor/generator 30 through a wire conductor. Depending uponthe stimulus desired, any number of electrodes may be used. Model 3387DBS™ electrodes sold by Medtronic, Inc. of Minneapolis, Minn. may beused. Stimulation electrodes 40 serve to produce a sensory experiencefor the patient based on the signal provided by the signalprocessor/generator 30. Under the embodiment of FIG. 1, the stimulationelectrodes 40 are placed along the spinal cord in the epidural space.The exact placement of the electrodes 40 is dependent upon the type ofsensory experience desired. Sensors may be placed to automaticallyelicit a visual, aural or touch stimulus. An alternative sound stimulusmay be an speaker mechanism as found in synchromed pumps. For example,Synchromed® model 8616 pump sold by Medtronic, Inc. may be used.Alternatively, sound may be generated via a piezoelectric soundgenerator. Alternatively, any combination of touch stimulus, sightstimulus and sound stimulus may be utilized.

In another application, a large sensory stimulus may be desired wherethe sensory stimulus in itself would serve to prevent the onset of aseizure. In such a case, electrodes 40 may be placed along theanterolateral aspect of the spinal cord to activate the pain fibers ofthe spinothalamic tract thereby creating a more painful experience.Alternative placement of electrodes 40 may include the dorsal column ofthe spinal cord, the antero lateral column of the spinal cord, skinnerves, the auditory cortex, the somatosensory cortex, nuclei of sensorythalamus, or the visual cortex.

Yet another arrangement is placement of the electrodes 40 over thesomatosensory cortex either by using peg electrodes in the skull (tosense EEG) or epidural electrodes slipped under the skull through a burrhole to stimulate the cortex. Still another option is use of a steerableelectrode to allow changes to the desired sensory stimulus. Such anelectrode is disclosed U.S. patent application Ser. No. 08/637,361 filedApr. 25, 1996 and entitled "Techniques for Adjusting the Locus ofExcitation of Neural Tissue in the Spinal Cord or Brain." As anotherembodiment, electrodes 40 may be placed directly under the skin toproduce skin senses.

In accordance with another embodiment of the present invention, thesystem includes generally a sensing portion, a signal generating portionand a therapy delivery portion. Under this embodiment, the sensingportion monitors electrical, chemical and/or physiological activity ofthe patient. The signal generating portion transduces the sensedactivity of the patient to a corresponding electrical signal used toactivate a pattern of sensation in one part of the sensory nervoussystem. The signal generating portion includes generally a signalgenerator. Under this embodiment, means for pattern recognition, such asalgorithms, would not be required. The sensed signal is processed andthe therapy delivery portion provides continuous sensory stimulation tothe patient representative of the sensed electrical, chemical and/orphysiological activity. Alternatively, the patient may receive sensorystimulus in intervals of short time periods. For example intervals of1-10 seconds may be utilized. Rather than provide the patient withsensory stimulation only when a possible seizure onset is calculated,the patient is provided continuous stimulation. The sensory stimulationprovided includes features which are in some way related to the featuresextracted from the EEG/ECoG containing the most power. The stimulusintensity which is determined by the pulse width and amplitude of thestimulus pulses might be related to the amplitude of the EEG/ECoG.Alternatively, stimulus amplitude might be related to a measure ofcomplexity as described by K. Lehnertz and C. E. Elger ("Neuronalcomplexity loss in temporal lobe epilepsy: effects of carbamazepine onthe dynamics of the epileptogenic focus.", Electroencephalography andclinical Neurophysiology, 103 (1997) 376-380. Over time and after one ormore seizure episodes, the patient will learn to recognize thestimulation patterns which are indicative of a seizure onset. The humanbrain which has an inherent ability to recognize patterns may therebylearn to recognize the patterns for the occurrence of seizures.

By using the foregoing techniques for electrical stimulation, seizurepatients may be provided adequate warning of a possible seizure onset toavoid the risk of physical injury. The patient may also take action toavoid the possible onset of the seizure. Those skilled in that art willrecognize that the preferred embodiments may be altered or amendedwithout departing from the true spirit and scope of the invention, asdefined in the accompanying claims.

I claim:
 1. A method of warning a patient of a possible onset of aseizure using a sensor, a signal generator and at least one implantableelectrode having a proximal end and a stimulation portion, the methodcomprising the steps of:surgically implanting the sensor within a bodyof a patient; coupling the sensor to the signal generator; surgicallyimplanting the electrode in the body, coupling the proximal end to thesignal generator, and positioning the stimulation portion to be incommunication with neural tissue within the body; and sensing aparameter of the body with the sensor and generating a sensing signal;processing the sensing signal by a pattern recognition means forrecognizing a pattern indicative of the onset of a seizure; and if thepattern is recognized, stimulating the neural tissue with the electrodeto generate a sensory stimulus to the body.
 2. The method of claim 1,wherein the step of surgically implanting the sensor includes the stepof positioning the sensor to be in communication with a predeterminedsite in a brain.
 3. The method of claim 2, wherein the step ofpositioning includes the step of selecting the predetermined site fromthe group consisting of the thalamus, internal capsule, hippocampus,cortex and basal ganglia.
 4. The method of claim 1, wherein the step ofsensing includes the step of sensing electrical activity of a brain. 5.The method of claim 1, wherein the step of sensing includes the step ofsensing chemical activity of a brain.
 6. The method of claim 1, whereinthe step of surgically implanting includes the step of surgicallyimplanting the signal generator.
 7. The method of claim 6, wherein thestep of surgically implanting the signal generator includes the step ofplacing the signal generator in a subclavicular, subcutaneous pocket ofthe body.
 8. The method of claim 6, wherein the step of surgicallyimplanting the signal generator includes the step of placing the signalgenerator in an abdomen of the body.
 9. The method of claim 1, whereinthe step of processing the sensing signal includes the step ofperforming an algorithmic operation.
 10. The method of claim 9, furthercomprising the step of changing the algorithmic operation to a secondalgorithmic operation.
 11. The method of claim 1, wherein the step ofstimulating includes the step of providing a type of stimulus selectedfrom the group consisting of touch stimulus, visual stimulus, and auralstimulus.
 12. The method of claim 1, wherein the step of surgicallyimplanting the electrode includes the step of positioning the electrodeto be in communication with a predetermined part of a spinal cord of thebody.
 13. The method of claim 12, wherein the step of positioningincludes the step of selecting the predetermined part from the groupconsisting of an epidural space, dorsal aspect, anterolateral aspect,and spinothalamic tract.
 14. The method of claim 1, wherein the step ofsurgically implanting the electrode includes the step of positioning theelectrode to be in communication with a somatosensory cortex of thebrain.
 15. The method of claim 1, wherein the step of surgicallyimplanting the electrode includes the step of positioning the electrodeto be in communication neural tissue underneath skin tissue of the body.16. An apparatus for warning a patient of a possible onset of a seizurecomprising:an implantable sensor capable of generating a sensing signal;a signal processor coupled to receive the sensing signal and havingmeans for signal processing, means for pattern recognition indicatingthe possible onset of a seizure, and a signal generator for generating astimulation signal; and at least one electrode having a proximal end andstimulation portion, the proximal end being coupled to receive thestimulation signal, the stimulation portion coupled to stimulate neuraltissue for delivering a sensory stimulus to the body.
 17. The apparatusof claim 16, wherein the implantable sensor comprises at least onesensing electrode.
 18. The apparatus of claim 17, wherein the sensingelectrode is selected from the group consisting of a peg electrode,epidural electrode, subdural electrode, and a subcutaneous electrode.19. The apparatus of claim 16, wherein the implantable sensor includes atransducer and a sensing electrode having an ion selective coating. 20.The apparatus of claim 16, wherein the implantable sensor has means forsensing physiological changes of a body.
 21. The apparatus of claim 16,wherein the means for signal processor includes an analog to digitalconverter, an amplifier and a filter.
 22. The apparatus of claim 16,wherein the means for signal processing includes a microprocessor. 23.The apparatus of claim 16, wherein the means for pattern recognitionincludes a microprocessor.
 24. The apparatus of claim 16, wherein thesignal processor is an external device further comprising means fortelemetrically communicating with the sensor and the electrode.
 25. Theapparatus of claim 16, wherein the electrode comprises a steerableelectrode.
 26. A method of warning a patient of a possible onset of aseizure using a sensor, a signal generator and at least one implantableelectrode having a proximal end and a stimulation portion, the methodcomprising the steps of:surgically implanting the sensor within a bodyof a patient; sensing a parameter of the body and generating a sensingsignal; coupling the signal generator to receive the sensing signal andto generate a therapy signal based on the sensing signal; surgicallyimplanting the electrode in the body, coupling the proximal end toreceive the therapy signal, and positioning the stimulation portion tobe in communication with neural tissue within the body; and periodicallystimulating the neural tissue to generate a sensory stimulus based onthe therapy signal.
 27. A method of preventing the onset of a seizureusing a sensor, a signal generator and at least one implantableelectrode having a proximal end and a stimulation portion, the methodcomprising the steps of:surgically implanting the sensor within a bodyof a patient; coupling the sensor to the signal generator; surgicallyimplanting the electrode in the body, coupling the proximal end to thesignal generator, and positioning the stimulation portion to be incommunication with neural tissue within the body; and sensing aparameter of the body with the sensor and generating a sensing signal;processing the sensing signal by the signal generator to recognize apattern indicative of the onset of a seizure; and if the pattern isrecognized, providing a sensory stimulus to the neural tissue with theelectrode to responsively initiate desynchronization of neural activity.28. The method of claim 27, wherein the step of providing sensorystimulus includes the step of stimulating a predetermined portion of theneural tissue, the predetermined portion being selected from the groupconsisting of a dorsal column of a spinal cord, an antero lateral columnof the spinal cord, skin nerves, auditory cortex, somatosensory cortex,nuclei of sensory thalamus, and visual cortex.